High frequency oscillation generators



June 13, 1967 K. D. FROOME 3,325,740

HIGH FREQENCY OSCILLATION GENERATORS Filed Dec, 29, 1964 United States Patent HIGH FREQUENCY OSCILLA'IION GENER kTORS Keith Davy Froome, Teddington, England, asslgnor to National Research Development Corporation, London,

England, a British corporation Filed Dec. 29, 1964, Ser. No. 421,834 Claims priority, application Great Britain, Jan. 3, 1964, 392/64 Claims. (Cl. 328-49) This invention relates to high frequency oscillation generators and is more particularly concerned with arrangements for generating energy at microwave frequencies, such as those described in co-pending patent application Ser. No. 342,002, filed Feb. 3, 1964 by K. D. Froome for High Frequency Electrical Oscillation Generators, by activation of a non-linear element, such as a plasma-metal junction, by a microwave input and extracting therefrom output power at harmonic frequencies of such microwave input.

In order to obtain maximum efliciency with such form of oscillation generator it is desirable, firstly, that all harmonic frequency currents as well as those at the fundamental input frequency should flow through the nonlinear element; secondly, that the harmonic frequency extraction means, such as a radiator, should have zero impedance to all of the harmonic frequencies except the particular one which is required; thirdly, that the harmonic output should be undamped and fourthly, that the microwave input drive at the fundamental frequency should be affected as little as possible by the changing load impedance which is presented by the non-linear element during each single cycle period of such fundamental input frequency.

Objects of the present invention include the provison of an improved constructional arrangement of increased operational efficiency by reason of compliance to substantial degree with some or all of the above-mentioned desirable conditions.

In accordance with one feature of the present invention the activated non-linear element is located at, or approximately at, the centre of a resonator having the form of a is made in two halves which can be adjusted slightly relative to one another in order to obtain optimum output at the required harmonic frequency.

According to another feature of the invention, an output hole or window is provided in the aforesaid hollow spherical resonator for the purpose of extracting harmonic frequency energy by transmission down a suitable guide or tube. By suitable restriction of the size of such a hole or window those harmonic frequencies which are of longer wave-length than that which is desired may be rejected thereby assisting in satisfying the second of the;

above quoted conditions.

Further aid in sastisfying the second of the above quoted conditions may be obtained by use of a further feature of the invention and in accordance with-which adjustable sheaths are provided around each of the elec-.

trodes or connection wires leading to the non-linear element which is located at the centre of the hollow resonator. Such sheaths may be either cylindrical or conical (tapering towards the centre of the sphere) and are each independently adjustable in an axial direction along the ice associated electrode or connecting wire to permit the formation of a low-Q resonator by the unsheathed projecting portion of such electrode or wire and the setting-up of standing waves at harmonic frequencies in such projecting portion due to the reflection caused by the sheath. Such low-Q resonator is in parallel with the high-Q resonator of the hollow sphere and greatly assists in reducing the number of harmonics which are radiated.

Yet a further feature of the invention relates to the provision of means for adjusting the position of the nonlinear element with respect to the geometrical centre of the hollow resonator in order to vary the degree of coupling between such spherical resonator and the standing waves in the unsheathed ortions of the projecting electrodes or connecting wires to said non-linear element. Such positional adjustment permits selective improvement of the generated power in any one particular harmonic relative to the other harmonics and further assists in satisfying the second of the above-mentioned conditions.

The provision of the third mentioned condition, i.e. an undamped harmonic output, may be adequately achieved if the Q-factor of the overall harmonic resonant circuit is greater than the order of the harmonic to be extracted and radiated. Since the spherical resonator has a radius (half of the fundamental wavelength) which is large in terms of the harmonic wavelength, 2. sufficient good Q- factor is automatically achieved.

As the spherical resonator of arrangement in accordance with the invention is resonant at the fundamental input frequency as well as at the harmonic frequencies, stored energy at such fundamental input frequency is always present within the resonator and operates to reduce to a minimum the effect of the changing impedance of the junction during each cycle at the fundamental frequency, and hence assists in meeting the fourth of the abovementioned conditions by reducing the effect of such changing load impedance on the microwave input drive.

In order that the above and other features of the invention may be better understood, one particular constructional embodiment thereof incorporating a plasmametal junction form a non-linear element will now be described by way of an illustrative example only and with reference to the accompanying drawing in which:

FIGURE 1 is a largely schematic diagram showing the basic elements of the arrangement described in copending application No. 342,002, while FIGURE 2 is an enlarged fragmentary cross section view showing the form of one construction according to the present invention.

Referring 'first to FIG. 1 of the drawing which shows the basic elements of the generator arrangement described in the aforesaid co-pending application, an input waveguide 11 of rectangular section is supplied with microwave energy at the chosen input frequency from an oscillation generator 62 of any suitable form such as a CW Klystron type generator operating in the Q-band, e.g. at 35 gc./ s. A tuning piston 16 is movable axially within the waveguide 11 by screw or other adjustment means indicated schematically by the knob 15. A second waveguide 12 of circular section forms the output waveguide for providing energy, at a harmonic frequency of the input generator 62, to a load 63.

This output waveguide 12 is also provided with a tuning piston 20 movable axially along the guide by screw or other adjustable means indicated schematically by the knob 19. The respective waveguides 11, 12 are set with their respective longitudinal axes at right angles to one another and are so positioned relative to one another that the plane of the lower major dimension'wall of the input guide 11 coincides in position with the plane which lies tangential to the adjacent nearest part of the wall'of 3 the output guide 12, communication between the two guides 11, 12 being provided by means of a circular hole 30 in the common wall region.

The hole 30 is positioned at a point coincident with the intersection of the two vertical planes which include the respective axes of the two waveguides and along the vertical line defined by such intersection of said planes is disposed the respective components of the non-linear element in the form of an arc assembly 21.

The are assembly takes the form of a lower very thin cathode electrode wire 22 (e.g. of platinum and of 0.008 inch diameter) surrounded by and slidable axially within the bore of a cylindrical cathode sheath 23 conveniently formed of molybdenum. The sheath 23 projects upwardly through a hole in the output waveguide 12 diametrically opposite the hole 30 and is adjustable axially to control the amount of its projection into such guide 12 by suitable screw or other means indicated schematically by the knob 26. The cathode wire 22 is likewise adjustable axially to control the extent of its further projection beyond the upper end of the cathode sheath 23 by further screw or other adjustment means indicated schematically by the knob 27.

The opposite or anode arc electrode is also in the form of a platinum wire 28 of greater diameter (e.g. 0.020 inch) than the cathode wire 22. This anode wire is carried within the bore of a cylindrical tuning plunger 31 of copper or other similar metal, the plunger 31 projecting slightly into the overlying input waveguide 11 with a capacitive coupling with such waveguide while the inner anode electrode wire 28 projects beyond the lower end of such tuning plunger across the minor dimension of the input waveguide 11 so as to be coupled to the input wave energy therein and through the communicating hole 30 to a position where its pointed lowermost end is closely adjacent the cathode electrode 22 within the output waveguide 12. The tuning plunger 31 is adjustable axially by screw or other means indicated schematically by the knob 32 while the position of the anode wire is similarly adjustable axially within the tuning plunger by further screw or other adjustment means indicated schematically by the knob 29.

The waveguides 11, 12 are hermetically sealed on each side of the arc region as by means of inserted quartz window plugs and packing gland arrangements around each of the variable electrode controls to allow the arc region at least to be filled with an inert gas, such as argon with the addition of between 4% and 15% of hydrogen, under an operating pressure of between 1,000 and 4,000 lbs. per square inch derived from a source 61. The lower cathode arc electrode and the waveguides are conveniently connected to ground and the upper anode electrode connectable by way of switch means 65, either to a DC. source 66 or to an A.C. source 67. The two waveguides are conveniently formed as bores in a solid metal 'block.

In the operation of such arrangement input microwave power from the source 62 supplies input energy to the waveguide 11. Initially, by the switch means 65, direct current is supplied to the arc electrodes 22, 28 from the source 66 with the lower electrode 22 as the cathode and a DC. are is struck between the opposing electrode ends as by suitable temporary alteration of the position of the cathode electrode. The operation of the arc results in the formation of a small ball of molten platinum at the lower end of the anode electrode 28 and this ball is allowed to alter in size until it becomes resonant at the desired one of the harmonic frequencies of the input source 62 from which it derives wave energy by reason of its extension across the input waveguide 11. When this resonance point is reached the D.C. energisation is rapidly changed to A.C.

energisation from the source 67, after which the arc maintains its constant resonance dimension and serves to proivide output energy at a chosen harmonic frequency, such as 1,015 gc./ t the load 63 from the output waveguide 4 The above device and its particular manner of operation is described in greater detail in the aforesaid copending application to which reference should be made for further information.

Referring now to FIG. 2 which illustrates the modified form of construction of the present invention, the input waveguide 11 of rectangular section is formed as in the previously described embodiment as a bore within a metal base block 10. A circular section bore at right angles to the bore 11 contains a thin walled circular section tube 40 resembling but not forming the output waveguide 12 of the earlier construction. The tube 40 coincides with the lower wall of the rectangular guide 11 at the point of intersection as in the earlier construction and is likewise provided with a communicating clearance hole 30.

The arc assembly, indicated generally at 21, comprises a very thin platinum wire (e.g. of 0.008 inch diameter) forming the cathode 22. This wire is carried within a cylindrical cathode sheath 23 of molybdenum. The sheath 23 projects through a close-fitting hole in the tube 40 diametrically opposite to the hole 30, and is connected by its outward end to an axially movable sleeve 24, such sleeve being part of screw or other adjustable means'which may conveniently be of the form as described for the corresponding element in the aforesaid co-pending application. The cathode wire 22 is likewise connected to screw or other adjustment means (not shown) for moving this wire axially relative to the sheath 23. Such screw or other adjustment means may conveniently also be as described in the aforesaid co-pending application.

The anode electrode 28 comprises a very thin platinum wire (also of 0.008 inch diameter) located coaxially within a surrounding cylindrical anode sheath 41 which is itself coaxially disposed within and axially adjustable with respect to a surrounding tubular tuning plunger 31. The position of the tuning plunger 31 is adjustable axially by screw or other means not shown and conveniently of a form as described for the corresponding element in the aforesaid earlier application. The anode sheath 41 is likewise connected to screw or other position adjustment means which may also resemble the means provided for the tuning plunger 31 while the anode wire 28 is likewise also connected to screw or other adjustment control means which may conveniently take the form of those described for the corresponding element in the aforesaid earlier application. The lower end of the plunger 31 is slidable within a surrounding metal sleeve 33 provided with a radial flange 34 at its lower end. This flange is in clamping contact with a mica sheet 35 interposed between the upper surface of the flange 34 and an opposing annular surface 10a in the metal block 10 to provide a decoupling capacitance between the sleeve 33, its electrically interconnected tuning plunger 31, sheath 41 and anode electrode 28 and the grounded metal block 10. The anode electrode and its associated parts are insulated from the base block 10 and the opposite end of the sleeve 33 is screw threaded into an insulating collar 36 which 'is mounted in a bore of the block 10 in a manner similar to that described in the aforesaid earlier application. The sheath 41 projects across the rectangular section input waveguide 11 at a point along its central axial plane in the direction of the minor dimension of the guide and then extends through the clearance hole 30 to terminate near the centre of the tube 40 with the coaxial anode wire 28 projecting beyond its lower end towards the coaxially disposed end of the cathode wire 22.

The opposing aligned tips of the two electrode wires 22, 28 between which the are forming the non-linear element is maintained, are located approximately at the centre point of a hollow sphere 44 defined by the innerv hemispherical surfaces 45 of the opposing ends of two piston-like elements 42, 43. These elements are each made of copper or like good conductivity metal and are each made adjustable axially within the tube 40 under the control of suitable screw or other adjustment means which, although not shown, may resemble those shown in the earlier application for controlling the position of the tuning piston 20. The piston-like element 42 is provided with an unbroken hemispherical surface 45 but the corresponding surface of the opposite piston-like element 43 is provided at its central point coincident with the axis of the tube 40, with a small, preferably circular, hole 47 forming an output window through which the output energy at a harmonic frequency of the input source is transmitted to the output guide 12 which is of circular cross section and is formed as a tubular extension from the piston element 43. The adjustment means for this piston element 43 may resemble those shown for the piston 20 of the earlier construction with suitable modification to permit the passage of the output waveguide 12.

The device described is provided with suitable sealing means in each waveguide and around each adjustment means and is arranged to be filled with gas under pressure during operation in a manner analogous to that described in the aforesaid co-pending aplication and is likewise provided with means for supplying suitable energizing currents to the respective arc electrodes as well as the requisite microwave input to the waveguide 11.

In the operation of this improved construction, the anode and cathode electrodes 22, 28 are supplied with either switched DC. or AC. preferably at about 5,000 c.p.s. as described in the earlier application whereby the electrodes periodically reverse polarity and hence continuously change their respective anode and cathode functions. The respective electrode wires 22, 28 are each adjusted to protrude by a fraction of one millimetre beyond their sheaths. The position of the arc with respect to the centre of the resonator chamber 44 may be altered by movement of both of the wire/sheath pairs jointly in the same sense while the size of the chamber itself may be adjusted slightly to obtain optimum results by movement of one or both of the two elements 42, 43. The tuning plunger 31 around the anode sheath 41 may be used to improve the input coupling from the input guide 11 to the resonator chamber 44 or, by suitable adjustment, it may be caused to act as a tunable choke to prevent leakage of a desired harmonic frequency from the resonant chamber to the anode sheath.

The inner surfaces 45 of the spherical chamber 44, in addition to being of good electrical conductivity, are preferably polished so as to reflect thermal radiation from the are back to such are or the arc electrodes, thereby to reduce the heat losses and in consequence the power needed to maintain the plasma of the arc.

The respective sheaths 23 and 41 have been shown and described as being of cylindrical shape with radial surfaced inner ends but such sheaths may be of conical shape tapering towards the point of emergence therefrom of the associated anode or cathode electrode wires.

The invention has been particularly described with relation to the use of a plasma-metal junction form of non-linear element for converting the input frequency energy to the required harmonic frequency energy, but the same basic principles and constructions are applicable to use with other forms of non-linear elements such as a non-linear resistance or a non-linear reactance, or a combination of both a non-linear resistance and a non-linear reactance.

I claim:

1. A high frequency electrical oscillation generator comprising resonant chamber forming means defining a hollow resonant chamber having a conductive spherical surface, a non-linear element located substantially at the centre of said resonant chamber, input wave energy conducting means arranged for connection to a microwave power source, coupling means between said nonlinear element and said wave energy conducting means for activating said non-linear element by wave energy from said microwave power source and means for extracting wave energy at a harmonic frequency of said microwave power source from said resonant chamber.

2. A high frequency electrical oscillation generator according to claim 1 in which said resonant chamber is slightly adjustable in size about a mean radius dimension equal to one half of the wavelength of said microwave power source.

3. A high frequency electrical oscillation generator according to claim 1 which includes an output aperture in said resonant chamber for extracting wave energy at a harmonic frequency of said microwave power source.

4. A high frequency electrical oscillation generator according to claim 1 in which said non-linear element is a plasma-metal junction.

5. A high frequency electrical oscillation generator according to claim 1 in which said resonant chamber forming means comprise a pair of opposed members each having a concave hemispherical surface on their facing ends.

6. A high frequency electrical oscillation generator according to claim 5 in which at least one of said opposed members is movable towards or away from the other member.

7. A high frequency electrical oscillation generator according to claim 1 in which said non-linear element is adjustably mounted to allow alteration of its position within said resonant chamber.

8. A high frequency electrical oscillation generator comprising resonant chamber means defining a hollow resonant chamber having a conductive spherical surface, a pair of electric arc electrodes defining an arc gap located substantially at the centre of said resonant chamber, input wave energy conducting means arranged for connection to a microwave power source, coupling means between one of said arc electrodes and said wave energy conducting means for activating said arc gap by wave energy from said microwave power source, a source of inert gas under pressure connected to provide at least said chamber with a gaseous filling at a pressure of at least 1,500 pounds per square inch and means for extracting wave energy at a harmonic frequency of said microwave power source from said resonant chamber.

9. A high frequency electrical oscillation generator comprising an input waveguide arranged for connection to a source of microwave power, a hollow spherical resonant chamber having a conductive wall surface which is slightly adjustable in size about a mean radius dimension equal to one half of the wavelength of said microwave power source, a plasma-metal junction located at the centre of said resonant chamber, input coupling means for activating said plasma-metal junction by wave energy in said input waveguide, an output waveguide, a source of inert gas under pressure connected to provide at least said chamber with a gaseous filling at a pressure of at least 1,500 pounds per square inch and means for extracting wave energy at a harmonic frequency of said microwave power source from said resonant chamber into said output waveguide.

10. A high frequency electrical oscillation generator according to claim 9 which includes a microwave oscillation generator operating at a frequency within the Q- band of frequencies connected to said input waveguide.

References Cited UNITED STATES PATENTS 2,240,941 5/1941 Ohl 331127 X 3,212,034 10/1965 Kaufman et al 315-39 X ARTHUR GAUSS, Primary Examiner.

I. ZAZWORSKY, Assistant Examiner. 

1. A HIGH FREQUENCY ELECTRICAL OSCILLATION GENERATOR COMPRISING RESONANT CHAMBER FORMING MEANS DEFINING A HOLLOW RESONANT CHAMBER HAVING A CONDUCTIVE SPHERICAL SURFACE, A NON-LINEAR ELEMEMT LOCATED SUBSTANTIALLY AT THE CENTRE OF SAID RESONANT CHAMBER, INPUT WAVE ENERGY CONDUCTIVE MEANS ARRANGED FOR CONNECTION TO A MICROWAVE POWER SOURCE, COUPLING MEANS BETWEEN SAID NONLINEAR ELEMENT AND SAID WAVE ENERGY CONDUCTING MEANS FOR ACTIVATING SAID NON-LINEAR ELEMENT BY WAVE ENERGY FROM SAID MICROWAVE POWER SOURCE AND MEANS FOR EXTRACTING WAVE ENERGY AT A HARMONIC FREQUENCY OF SAID MICROWAVE POWER SOURCE FROM SAID RESONANT CHAMBER. 